As the owner of a mac with an amd gpu, I'm very excited to see support coming soon. Been wanting to get into ml but been pretty discouraged with all of the popular libraries being cuda-only.
Actually, if you're adventurous, you can clone it from github and build on your mac with bazel, but, your experience may suck in terms of performance (that's why it's not officially released yet). But, because you have an AMD, it will probably work well.
You would need to:
bazel build -c opt plaidml:wheel plaidml/keras:wheel
You would need to: bazel build -c opt plaidml:wheel plaidml/keras:wheel
and then
sudo pip install bazel-bin/plaidml/whl bazel-bin/plaidml/keras/whl